This is the pictograph of a double-headed drum combined with two diagonal lines that resemble the Chinese character bā 八. Bā can mean all around or on all sides, which is the
interpretation that I think applies here. Hence, this Indus sign is an ideograph for the sound of a reverberating drum.

Illustrative Text Reference:

Allahdino: Seal: Ad-6 A (NB. The inscription would be the mirrored image of that seen in photograph Ad-6 A): Sayid Ghulam Mustafa Shah and Asko Parpola, 1991: Corpus of Indus Seals and
Inscriptions: Volume 2: Page 388: Collections in Pakistan: Suomalainen Tiedeakatemia.

Comment:

Inscription Ad 6 is interesting because it may refer to a signal drum that was used for timekeeping. In Chinese cities, a drum was sounded at dusk. It is possible that the people of Allahdino had
the same custom.